Rubber articles made from natural or synthetic rubber include surgical gloves, physician examining gloves, industrial work gloves, prophylactics, catheters, balloons, tubing, sheeting and the like. Some of these articles, and in particular gloves, require the ability of donning, that is, the ability of the rubber article to be slid on and off skin surfaces without undue clinging or friction. Surgical gloves require wet donning, that is, the ability to be slid over wet skin surfaces, while physician examining and industrial work gloves require the ability to be slid over dry skin surfaces. Other rubber articles, like catheters and tubing, require some means to isolate the rubber from body fluids and tissue.
While this invention pertains to polymeric coatings for all rubber articles, discussion of the invention will focus on gloves, which are the most complex of rubber articles in terms of use and manufacture. To achieve acceptable donning properties, the surface of rubber a glove that comes in contact with skin or tissue has to be modified to reduce friction.
Surgeons' gloves, as of today, desire the donning surface to be sufficiently hydrophilic to absorb moisture that may be present on the surface of skin or tissue when the article is donned. Hydrogel coatings, as described, for instance, in U.S. Pat. No. 3,813,695, incorporated herein by reference, have been employed to achieve this property.
Examination and other gloves, by contrast, do not have a hydrophilicity requirement but still require the ability of the rubber article to be slid over dry skin surfaces with minimal drag or friction. Traditionally, this had been achieved by applying talc or other powdered materials, such as modified corn starch, over the skin or tissue-contacting surface of the glove. However, talc can no longer be used, and other powders can contaminate the field of work. The same problems arise for gloves used by workers in dust-free environments, such as clean rooms used in the manufacture of computer chips and other electronic articles.
With reference to FIG. 1, the conventional way of manufacturing rubber gloves has been to dip a mold or former, having the shape of the article to be formed, into a powder/coagulant slurry containing calcium nitrate and calcium carbonate. After drying, the mold is immersed in a rubber emulsion (latex) for a time sufficient for the rubber to coagulate and form a coating of desired thickness. The formed coagulated rubber article is then oven-cured. Water leaching is generally employed as the next step in order to remove rubber impurities. Once the leaching process has been completed, the rubber article is then dipped into a starch slurry. The starch-coated surface is then dried to provide a powder coat on the surface of the glove. After cooling, the rubber article is stripped from the mold. This turns the glove inside out. The mold is then cleaned and recycled.
Methods and materials used for glove manufacture are described, for instance, in U.S. Pat. Nos. 3,411,982 and 3,286,011 to Kavalier et al., both incorporated herein by reference, "Polyurethane Latexes for Coagulation Dipping," Sadowski et al., Elastomerics, August 1979, pp. 17-20, incorporated herein by reference, and "Dipping with Natural Rubber Latex," Pendler et al., Natural Rubber Technical Bulletin, 1980, also incorporated herein by reference.
Halogenation, for example, chlorination, and other chemical surface treatments have been used to eliminate the need for a powder coat that improves the dry donning characteristics of the final product. While effective, such treatments are expensive and have the shortcoming of reducing the shelf life of the rubber articles formed. It would be desirable to provide a rubber article with a powder-free donning surface without resorting to the expensive and article-deteriorating practices now popular. Such a process could substantially reduce the cost of manufacture and maximize the shelf life of the rubber article.
U.S. Pat. No. 4,302,852 to Joung, incorporated herein by reference, proposed covalently bonding an RTV silicone coating to the interior surface of a rubber surgeons glove after formation of the glove. This is said to reduce but not eliminate the need for a donning powder.
U.S. Pat. No. 4,304,008 also to Joung and incorporated herein by reference, applies a covalently bonded silicone or urethane to the outer surface of the glove, and halogenates the inner surface. The halogenated inner surface eliminates the need for a donning powder.
U.S. Pat. No. 4,310,928, also to Joung and incorporated herein by reference, teaches the deposition of a lipo compound (lipid or lipophilic substances) in place of a powder of mineral origin in combination with a surfactant in a coagulant solution to form a uniform film on a glove mold onto which the rubber is coagulated. The lipo compound and surfactant enable stripping of a formed glove from its mold.
These and other proposals have not achieved commercial acceptance.